[llvm] [RISCV] Support isel for Zacas for XLen and i32. (PR #77666)

[Yingwei Zheng via llvm-commits]

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@@ -2154,17 +3306,35 @@ define void @cmpxchg_i32_monotonic_monotonic(ptr %ptr, i32 %cmp, i32 %val) nounw
 ; RV64I-NEXT:    addi sp, sp, 16
 ; RV64I-NEXT:    ret
 ;
-; RV64IA-LABEL: cmpxchg_i32_monotonic_monotonic:
-; RV64IA:       # %bb.0:
-; RV64IA-NEXT:    sext.w a1, a1
-; RV64IA-NEXT:  .LBB20_1: # =>This Inner Loop Header: Depth=1
-; RV64IA-NEXT:    lr.w a3, (a0)
-; RV64IA-NEXT:    bne a3, a1, .LBB20_3
-; RV64IA-NEXT:  # %bb.2: # in Loop: Header=BB20_1 Depth=1
-; RV64IA-NEXT:    sc.w a4, a2, (a0)
-; RV64IA-NEXT:    bnez a4, .LBB20_1
-; RV64IA-NEXT:  .LBB20_3:
-; RV64IA-NEXT:    ret
+; RV64IA-WMO-LABEL: cmpxchg_i32_monotonic_monotonic:
+; RV64IA-WMO:       # %bb.0:
+; RV64IA-WMO-NEXT:    sext.w a1, a1
+; RV64IA-WMO-NEXT:  .LBB20_1: # =>This Inner Loop Header: Depth=1
+; RV64IA-WMO-NEXT:    lr.w a3, (a0)
+; RV64IA-WMO-NEXT:    bne a3, a1, .LBB20_3
+; RV64IA-WMO-NEXT:  # %bb.2: # in Loop: Header=BB20_1 Depth=1
+; RV64IA-WMO-NEXT:    sc.w a4, a2, (a0)
+; RV64IA-WMO-NEXT:    bnez a4, .LBB20_1
+; RV64IA-WMO-NEXT:  .LBB20_3:
+; RV64IA-WMO-NEXT:    ret
+;
+; RV64IA-ZACAS-LABEL: cmpxchg_i32_monotonic_monotonic:
+; RV64IA-ZACAS:       # %bb.0:
+; RV64IA-ZACAS-NEXT:    sext.w a1, a1
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dtcxzyw wrote:

Is the `sext.w` required? Can we mark `amocas.w` as a W user/producer?

https://github.com/llvm/llvm-project/pull/77666